Database Reference
In-Depth Information
MyApp2 m = new MyApp2();
MyRef useRef = new MyRef();
m.setRef( useRef );
ARRAY mA = m.getArray();
myRef = new MyRef();
}
Notice one last thing in the
main()
method definition. It sets the value of the static
myRef
member to
an instance of
MyRef
. From a static method, only static members of the class can be referenced. If we
tried to set the value of
myArray
from within
main()
, we would get an error at compile time, because until
we create an instance of
MyApp2
, there is no
myArray
member—it is not
static
.
Public and Private Modifiers
public
and
private
modifiers can exist on both methods and member variables. These help delineate
the items in a class that the user of a class has direct access to, from those items that the user of a class
cannot see (directly). These are
scope modifiers. That is the important thing about
public
and
private
: it
is important because it has some implications for security that we will discuss later.
In Listing 3-3, the
myArray
member is private, so someone using this class cannot get or modify
myArray
directly. However, we have provided the method
getArray()
which is public and can return
myArray
to anyone.
private ARRAY myArray = null;
static MyRef myRef;
public ARRAY getArray() {
return myArray;
}
void setRef( MyRef useRef ) {
myRef = useRef;
}
By default, methods and members, like the
myRef
member and the
setRef()
method, which are not
declared as
private
or
public
, are generally only accessible to other classes that come from the same
package. One additional scope modifier is
protected
. Protected scope is like the default, except it allows
you to permit subclasses of your class that are defined outside your package to see your members and
methods.
One design pattern (approach) declares all the class member variables are
private
, then sets about
establishing getters and setters (public methods that provide a way for other objects to get or set the
private members) to read from and write to the members. This is a feature of JavaBeans, and often of
Enterprise Java Beans, and lends to their usefulness as components in an IDE. They can be distributed
and incorporated into an IDE or application server without prior knowledge or definition by virtue of
their getters and setters—by reflection (or XML definition), the IDE can list the public getter and setter
methods of a bean
and provide access to the private members.
We have provided a getter method in our example code for the
myArray
member:
getArray()
. We
have also provided a setter method for the
myRef
member:
setRef()
; although, our method names don't
conform to JavaBeans standards, because we are not writing JavaBeans, and we needn't implement all
that boilerplate code.
